Oscillating system



1943- w. H. c. HIGGINS OSCILLATING SYSTEM Original Filed July 26. 1959 lNVEA/TOP W H. C. H/GG/NS ATTORNEY Patented Feb. 9, 1943 William H. C. Higgins,

York

West Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New Original application July 26, 1939, Serial No.

286,682, now vember 4, 1941. September 30, 1941,

4- Claims.

The invention relates to ultra-high frequency radio transmitters and more particularly to arrangements for adjusting and tuning such transmitters.

This application is a division of my copendi-ng application Serial No. 286,682, filed July 26, 1939, Patent No. 2,261,879, issued November 4, 1941-.

A feature of the invention is a tuning arrangement comprising a pair of Lecher wires of fixed length and means for varying the impedance between the said wires over a portion of their length, the proportionate part so modified being made variable for the purpose of tuning the system to a desired frequency.

In the accompanying drawing.

Fig. 1 shows a frequency-modulated ultra-high- !requency radio transmitter embodying the invention, the representation being partlyschematic and partly in detail;

Fig. 2 shows an elevation ofa mechanical arrangement appearing in partial plan view in Fig. l, for adjusting the coupling between a Lecher wire system and a coaxial line feeding an antenna, viewed as indicated by arrows 2-2 in Fig. 1; and

Fig. 3 shows across section of a by-pass condenser appearing in longitudinal section in Fig. I viewed as indicated by arrows 3-3 in Fig. 1.

The radio transmitter. of. Fig. 1,.which is illustrative of a system embodyingv the invention, is particularly adapted for use in a radiant energy distance indicating system. The transmitter generates an ultra-high frequency carrier wave which for the purposes of the distance indicating system is frequency modulated by means of a motor-driven variable condenser which cyclically varies the frequency over a fixedrange of values at a uniform rate. A distance indicating system employing a transmitter of this type is disclosed and claimed in a copending application of R. C. Newhouse, Serial No. 240,739, filed November 16, 1938.

The transmitter contains a vacuum tube having a cathode ll, an anode l2 and a grid I3 and mounted between two pairs of Lecher wires 14, I5 and l6, 11, respectively, all preferably enclosed in a shield or metallic box [3. The tube and wires constitute the principal components of an oscillatorof a conventional type. A coupling loop 19 is provided within the box for taking electrical output from the oscillator and supplying itby means of a coaxial line 20 to an antenna or doublet 2|. One end of the loop I9 is connected to the inner conductor of line20 and one branch of doublet 2! while the other end of the Patent No. 2,261,879, dated No- Divided and this application Serial No. 412,940

loop is connected to the inner conductor of an.- other coaxial line 22, the length of which may be adjusted for tuning purposes by moving a short-eircuiting plug 23 with the aid of a knob 24. The outer conductor of line 20 is connected. to the remaining branch of doublet 2|. Preferably the loop I9- is short length of the wires Ht, l5, and is located close to the. shield lfi near the. ends of wires 14 and.

IL5 where the current intensity in these wires is a maximum. The connections to the lines 20 and 22 from the loop ends are preferably short and they extend through apertures inthe shield 18. The outer conductors of the lines 20 and 22 are connected to the shield.

The coupling loop. I9 is preferably a u-shaped piece of flexible metal. and may be attached to the shield. ill by fixed, insulated supports. at the two ends. Referringto Figs. 1 and 2,.a screw 68. is. attached by means of an insulating link 69 to the. central portion of loop. IS in any suitable manner. Athumb-nut l0; fits into a hole in shield H3 and. engages: screw means for deforming the loop. by raising or lowering the central portion so that the coupling may be adjustedv from theoutside of the shield. Many other mechanical. linkages may beused to provide remote. control of the loop 19 and. a suitable arrangement will be readily supplied by one skilled in the art to meet requirements in any particular case;

Provision is made. for frequency modulation of the transmitter by means of a variable condenser 25 connected between. the Lecher conductors. l4 and. lb. The condenser is rotated at a uniform rate by a motor 26 which is in turn driven by a generator 21'. The motor is preferably asplit phase. synchronous motor with two windings which are supplied with currents in substantially quarter phase relation by means including a phasing: condenser 28;

The oscillator may be tuned over a range of operating frequencies by a tuning mechanism comprising a metallic rod or conductorii-fl mounted between the Lecher wires l6 and I l and extending throughv an aperture in the shield 18. The length of rod projecting within the shield may be adjusted by sliding the rod 3'0 in or out with the aid of a knob 31. The rod 39 may be locked in any desired position by means of a clamp 32 and a clamping screw 33. The rod 30 is preferably conductively connected to the shield 13 through the clamp 32' or by a snug'fit in the aperture through which the rod passes", but may, if desired, be insulated from the shield.

compared with the- 68 to provide a The filament supply current for tube E is introduced through a coaxial line comprising an outer conductor 34 and an inner conductor 35 con nected respectively to the terminals of a battery 36 or other suitable source of current. The length of the coaxial line 34, 35 is preferably somewhat less than a quarter wave-length of the mean operating frequency of the transmitter.

The plate current for tube is supplied by a battery 44 or other suitable source through a lead 45 and an insulated bushing to an enlargement 48 on the Lecher wire I 6. A grid leak path is provided by a connection from an enlargement 50 on Lecher wire I! through a grid leak resistor 46 having an adjustable portion 41. The enlargement 48 is in the form of a metallic plate which is insulated from shield l3 by a sheet 49 of mica. or other insulation. The plate 48, insulator 49 and shield 18 together form a condenser which efiectively connects wire l3 to ground at frequencies in the operating range. The similar plate 50 and an insulator 5! form another condenser together with shield ill for grounding the wire 11. Similar by-pass condensers are preferably provided between the shield l8 and the ends of the Lecher wires l4 and I5 remote from the tube Hi. One end of the coaxial conductor 34 is likewise provided with a plate 52 and an insulator 53 forming together with shield IS a condenser for grounding the outer conductor of the line at the operating frequencies. The insulator 53 is particularly useful when an alternating current source is substituted for battery 36 in which case it would be undesirable to have a direct current ground connection to the outer conductor 34. When a direct current source is employed, the insulator 53 may usually be omitted and the outer conductor 34 directly connected to the shield l3. Inner conductor 35 is similarly connected to the shield I8 by a by-pass condenser comprising a plate H attached to the conductor, and an insulator 12. The elements H and 12 are mounted on the outside surface of shield l8 and the latter forms one plate of the condenser as in the other by-pass condensers described above.

To permit tuning the cathode-ground circuit, a condenser is arranged having a fixed plate 37 connected to outer conductor 34 at the tube end, and a movable plate 38. A shaft attached to plate 38 is threaded through a bearing 39 and is rotatable by means of an insulating rod 40 having a screw-driver slot 4| in one end, projecting from an aperture in shield I 8. Rotation of shaft 4!! controls the spacing between plates 3'! and 38, thereby varying the capacity between them. This variable capacity may be adjusted to resonate with the inductive reactance existing between the filament end of conductor 34 and shield 18. Due to the close coupling between the conductors 34 and 35, the inductive reactance between the conductor 35 and the shield I8 is also resonated at the same time. Where this coupling is insufficient a by-pass condenser may be added between the filament end of conductor 35 and the filament end of conductor 34. To provide suflicient friction to retain the movable plate 38 in any desired position, a section 42 of fibre is inserted into the bearing 39. The plate 38 is grounded through the bearing 39 and a mounting bracket 43 which is fastened to the shield I 8.

The rotorof the variable condenser is coupled to the shaft 55 of the motor 26 through an insulating section 54. The motor is generally provided with ball bearings 56. It has been found by experience that high frequency currents from the Lecher wires 14, l 5 pass through the capacity path comprising the metallic portion of condenser 25, the insulating shaft 54 and the shaft 55 of the motor 25 and through the ball bearings 56 to ground. Fluctuations in the output of the oscillator are encountered due to variations in the impedance of the path including the ball bearings or other moving portions of the motor. Accordingly a high frequency by-pass is provided comprising a condenser having one plate consisting of a metallic band 51 attached to the lower end of shaft 54 and a second plate comprising a metal collar or shield 58 surrounding band 5'! but separated therefrom by a small air space. The shield 53 is connected to the shield It by means of a flange 59. The shield may be made in two parts for convenience in assembly.

Provision is made for determining the frequency generated by the oscillator. For this purpose a connection 30 is made to the outer conductor 34 of the coaxial line at a point selected to give a desired small voltage. The connection is extended by a lead 3| through a terminating resistor I3 and a coaxial line 62 to a wave meter 63.

To adjust the oscillator for a desired operating frequency, the position of rod 30 is varied until the desired frequency is obtained as shown by the wave meter 63. Moving the rod further into the interior of the shield raises the operating frequency and withdrawing the rod lowers the frequency. The rod may be locked in adjusted position by means of the clamp 32 and screw 33. The spacing between the condenser plates 3'! and 38 may then be adjusted by means of a screwdriver in slot 4| -to secure a maximum output from the transmitter consistent with the rating of the tube I 0. The antenna circuit may then be tuned to the operating frequency by sliding plug 23 with the aid of knob 24, preferably with loose coupling, and the coupling may thereafter be adjusted to any desired operating value.

The adjustment of the impedance of the Lecher wires I3, I! is made Without changing the effective length of these wires and in this respect differs from the usual practice. The wires I6 and 11 are fixed in length and the inductive reactance is varied by varying the amount of the rod 35 extending inwardly through the shield 18. The presence of the rod 30 controls the characteristic impedance of the adjacent section of the Lecher system and the value of this impedance in turn controls the effective impedance of the Lecher system. The wires l4, 15 are also fixed in length and are somewhat less than a quarter wave-length of the average operating frequency for which the oscillator is designed, but it has been found unnecessary to adjust the tuning of wires l4, l5, adjusting the rod 30 being all that is usually required. However, in general it is desirable that the complete Lecher system l4, l5, I6, I! shall be efiectively a half Wave-length long with the tube It) in the electrical center.

When the motor 26 is operated, the variable condenser 25 is rotated at a constant rate to produce a continual frequency modulation of the transmitter. High frequency currents which would tend to flow into the motor and to ground the by-pass condenser is shown in cross-sectional View in Fig. 3.

It will readily occur to those skilled in the art of ultra-high frequency signaling that the several features of the invention are applicable to many systems other than the transmitter herein illustrated and in various other situations where the functions involved may be utilized.

What is claimed is:

1. An oscillating system adjustable as to frequency, comprising a vacuum tube having a cathode, an anode and a grid, a pair of Lecher wires of fixed dimensions connected at one end to the anode and grid, respectively, said tube and said Lecher system being enclosed within a conductive shield of fixed dimensions, capacitative connections from the Lecher wires to the shield at the end remote from the tube, a third conductor projecting into the interior of the shield and extending adjacent to but spaced from said Lecher wires, and means for varyin the length of said third conductor so projected, thereby varying the resonant frequency of the system.

2. A tpning arrangement comprising a pair of spaced conductors having distributed capacity therebetween, a conductive shield substantially enclosing said spaced conductors, a third conductor projecting into the interior of said shield and extending adjacent to but spaced from said spaced conductors and means for varying the length of said third conductor so projected, thereby varying the resonant frequency of the system.

3. A tuning arrangement comprising a pair of Lecher conductors of fixed length, a conductive box substantially enclosing said Lecher conductors, a third conductor projecting into the interior of said box and extending adjacent to but spaced from said Lecher conductors and means for varying the length of said third conductor so projected, thereby varying the resonant frequency of the system.

4. A tuning arrangement parallel conductors of fixed length, a conductive shield substantially enclosing said parallel conductors, a third conductor projecting into the interior of said shield and extending parallel to said first-mentioned parallel conductors and between the same and means for adjusting the length of the portion of said third conductor lying between said conductors to vary the resonant frequency of the system.

comprising a pair of WILLIAM H. C. HIGGINS. 

